This invention is concerned with electrical energy monitoring circuitry and more particularly with electronic circuitry for measuring the amount of energy consumed by a system, displaying the corresponding cost of the energy and controlling and monitoring the resultant cost against a predetermined standard.
In the last few years, dramatic increases in the price of natural gas and oil have resulted in sharp rises in the cost of electricity for consumer use. Various incentives and programs have been pursued by state and federal governments and other institutions for the purpose of eliminating the waste of energy and developing more efficient energy sources. The consuming public, especially homeowners and industrial users of electrical energy, have become increasingly conscious of the need for energy conservation.
In spite of the foregoing developments, it has been difficult if not impossible for a consumer of electrical energy to readily and continually monitor the amount of energy he is using. The resulting cost is normally not made available to the user until a monthly statement is received, some time after the electrical energy is consumed and the charges are incurred. This delay can be especially damaging during periods of high power consumption or in situations where power consuming appliances or apparatus are inadvertently left running for long periods of time.
It is possible for a consumer to manually monitor his electrical energy consumption through periodic readings of his electric meter and to calculate the charges, but the procedure is difficult and cumbersome and is therefore not practical. Moreover, present systems do not provide for feedback control to reduce, moderate or shut off the electrical power input when the maximum desired energy usage has been reached.
The present invention provides a system for generating and displaying to the consumer the cost of electrical energy being used and for monitoring or controlling the amount of energy consumed over a given period of time. The circuit senses the electrical power flowing into the system and generates a digital signal representative of the amount of electrical power being received. Accumulator means count the digital signal pulses during a predetermined period of time. When the count exceeds a designated maximum, an output signal is generated which can be used to actuate alarm or control circuitry.
In a more specific embodiment of the present invention, electronic circuitry is provided for monitoring the amount of electrical energy consumed by a system over an input bus during a given period of time. An electromagnetic circuit senses the magnitude of the input current and generates a d-c voltage having an amplitude representative of the magnitude of the input current. A voltage-controlled oscillator is driven by the d-c voltage to generate an a-c signal having a frequency corresponding to the amplitude of the d-c voltage. The a-c signal is fed to a multivibrator which generates a pulse train having a frequency corresponding to the frequency of the a-c signal. The oscillator and multivibrator are preset so that the resultant pulse train corresponds to a unit cost of electrical energy.
The pulse train is fed to a series of digital counters which count the number of pulses generated. The counters are connected through decode circuitry to a display unit which continually reads out the cost of the electrical energy being consumed. The counters are sensed to generate an output signal in response to the count reaching a predetermined value. An alarm circuit is responsive to the output signal to indicate that the maximum desired amount of electrical energy has been consumed for a given period of time.
The above invention has a number of advantages for an electrical energy consumer. The on-line monitoring system provides up-to-date information to the consumer regarding his energy usage. Data concerning cumulative energy costs are generated and continually displayed. The alarm circuitry provides a warning when desired costs are exceeded, and the control circuitry can automatically modify or discontinue electrical service at that point. The system is easily connected to incoming power lines by electromagnetic means, and is compact and portable to accommodate a variety of applications.